This invention relates to a method for determining the mass flow rate of solids into a cyclone separator for a fluidized bed reactor and, more particularly, to such a method in which the solids mass flow rates are determined by measuring the gas pressures at various locations relative to the separator.
Fluidized bed reactors including combustors, gasifiers, and steam generators are well known. In these arrangements, air is passed through a bed of particulate material, including a fossil fuel, such as coal, and an adsorbent for the sulfur generated as a result of combustion of the coal, to fluidize the bed and to promote the combustion of the fuel at a relatively low temperature. The fluidized bed reactor thus offers an attractive combination of high heat release, high sulfur adsorption, low nitrogen oxides emissions and fuel flexibility.
Some fluidized bed reactors utilize what is commonly referred to as a bubbling fluidized bed in which a bed of particulate materials is supported by an air distribution plate, to which combustion-supporting air is introduced through a plurality of perforations in the plate, causing the material to expand and take on a suspended, or fluidized, state. The heat produced by combustion within the fluidized bed is utilized for various purposes such as to raise the temperature of a heat exchange medium, such as water, to generate steam.
In an effort to extend the improvements in combustion efficiency, pollutant emissions control, and operation turn-down afforded by the bubbling bed, a fluidized bed reactor has been developed utilizing a fast, or circulating, fluidized bed. According to this technique, higher fluidized bed densities are attained which is well below those of a typical bubbling fluidized bed. The formation of the low density circulating fluidized bed is due to its small particle size and to a high solids throughput. The velocity range of a circulating fluidized bed is between the solids terminal, or free fall, velocity and a velocity which is a function of the throughput, beyond which the bed would be converted into a pneumatic transport line.
In these circulating fluidized bed arrangements, a cyclone separator is often provided for receiving a mixture of gases, essentially comprising the fluidizing air and products of combustion, along with some entrained solid particles from the fluidized bed (hereinafter termed "solids"). The cyclone separator functions to separate the entrained solids from the gases and route the gases to a heat recovery area and the solids back to the furnace section of the reactor.
In these arrangements, it is very important to determine and regulate the mass flow of the solids into the separator, since this flow affects other important operational parameters of the reactor. However, to date there has been no effective, relatively inexpensive, technique for determining the solids mass flow rate into the cyclone separator.